ATM A Hearty Thanks to Peter Smith!

[Roger Ceragioli <rogerc@as.arizona.edu>]

Thank you so much, Peter, for your excellent web material concerning 
Ronchi matters!  This is of great value!

What I have seen in my own recent testing is very much in accord with 
your photos and simulations.  And if one will look even at Mike 
Spooner's excellent 8" f/5 mirror (tested in autocollimation) and really 
scrutinize the Ronchi bands, you can see small (presumably) diffraction 
effects at the edges, even though he was using a 100 ln/in. grating.  A 
200 ln/in grating would have showed them even better.  Knowing Mike 
personally, as I do, I absolutely trust his judgement concerning the 
quality of his mirrors.

But I don't automatically know which Ronchi band deformations in WHAT 
MAGNITUDE are acceptable.  And that has been my problem all along.

So many thanks also for simulations of what turned edges should do to 
the shape of the bands.  These simulations are even more helpful.  In 
fact, if one could compile a kind of illustrated manual of what Ronchi 
bands should look like for both spherical and parabolic mirrors, with 
and without various aberrations and zones, that would be exceedingly 
useful for ATMs and professionals too!  Malacara's chart just doesn't 
show enough possibilities.  I know that's a lot to ask, but dummies like 
me who can barely use a computer, much less download, extract and learn 
new programs would be highly grateful for this assistance.

Best regards,
Roger Ceragioli